Such illumination systems are known per se. They are used, inter alia, as luminair for general lighting purposes, for example, for office lighting or shop lighting, for example, shop window lighting or lighting of (transparent or semi-transparent) plates of glass or (transparent) plates of glass or (transparent) synthetic resin on which items, for example jewelry, are displayed. In addition, such illumination systems are used for general lighting purposes, such as for large-area direct-view light emitting panels such as applied, for instance, in signage, contour lighting, and billboards.
Such known illumination systems are also used as backlight-emitting panels in (image) display devices. Such illumination systems can particularly suitably be used as an illumination source in non-emissive displays, such as liquid crystal display devices, also referred to as LCD panels, which are used in, for example, television receivers, (computer) monitors, (cordless) telephones and portable digital assistance. The illumination systems can also be used in, for example, projection systems such as a digital projector, or so-called beamer, for projecting images or displaying a television program, a film, a video program or a DVD, or the like.
Such an illumination system is, for example, disclosed in EP 1 521 235 A2. The illumination system comprises a two-dimensional array of light emitting diodes (further also referred to as LEDs) placed on a rear panel of the illumination system. In an embodiment of the illumination system in the cited document, the LEDs all emit light of substantially the same color, for example, a primary color blue. The illumination system further comprises a layer of color-converting phosphor which is arranged on a cover plate of the illumination system, resulting in a so-called remote phosphor configuration. The phosphor layer is a uniform layer, for example, comprising a phosphor Yttrium Aluminum Garnet (further also indicated as YAG:Ce), converting light of the primary color blue into light of a primary color yellow. The layer may be a film with uniform density of particles or a luminescent dye distributed throughout the film. Some of the light of the primary color blue emitted by the LED is transmitted by the phosphor layer so that yellow and blue light components both are transmitted to the display device for illuminating the display device. The illumination system comprising blue LEDs can be used for a large range of different displays, with different types of color filters. By changing the thickness of the phosphor layer and/or the concentration of the phosphor in the phosphor layer, the light emitted by the illumination system can be optimized to fit a particular LCD.
A drawback of the known illumination system is that a color temperature of the light emitted from the display device is too low.